Field of the Invention
This invention relates to Multifunctional Viscosity Modifier (MFVM) additives for petroleum oils particularly lubricating oils, their functionalized intermediates, and methods for making both.
Multigrade lubricating oils typically are identified by two numbers such as 10W30, 5W30 etc. The first number in the multigrade designation is associated with a maximum low temperature (e.g., -20.degree. C.) viscosity requirement for that multigrade oil as measured typically by a cold cranking simulator (CCS) under high shear, while the second number in the multigrade designation is associated with a minimum high temperature (e.g., 100.degree. C.) viscosity requirement. Thus, each particular multigrade oil must simultaneously meet both strict low and high temperature viscosity requirements in order to qualify for a given multigrade oil designation. Such requirements are set e.g., by ASTM specifications. By "low temperature" as used herein is meant temperatures of typically from about -30.degree. to about -5.degree. C. By "high temperature" as used herein is meant temperatures of typically at least about 100.degree. C.
The minimum high temperature viscosity requirement, e.g., at 100.degree. C., is intended to prevent the oil from thinning out too much during engine operation which can lead to excessive wear and increased oil consumption. The maximum low temperature viscosity requirement is intended to facilitate engine starting in cold weather and to ensure pumpability, i.e., the cold oil should readily flow or slump into the well for the oil pump, otherwise the engine can be damaged due to insufficient lubrication.
In formulating an oil which efficiently meets both low and high temperature viscosity requirements, the formulator may use a single oil of desired viscosity or a blend of two lubricating oils of different viscosities, in conjunction with manipulating the identity and amount of additives that must be present to achieve the overall target properties of a particular multigrade oil including its viscosity requirements.
The natural viscosity characteristic of a lubricating oil is typically expressed by the neutral number of the oil (e.g., S150N) with a higher neutral number being associated with a higher natural viscosity at a given temperature. In some instances the formulator will find it desirable to blend oils of two different neutral numbers, and hence viscosities, to achieve an oil having a viscosity intermediate between the viscosity of the components of the oil blend. Thus, the neutral number designation provides the formulator with a simple way to achieve a desired base oil of predictable viscosity. Unfortunately, merely blending oils of different viscosity characteristics does not enable the formulator to meet the low and high temperature viscosity requirements of multigrade oils. The formulator's primary tool for achieving this goal is an additive conventionally referred to as a viscosity index improver (i.e., V.I. improver).
A monofunctional V.I. improver is conventionally an oil-soluble long chain polymer. A multifunctional VI improver (MFVI or alternately MFVM) is an oil soluble polymer which has been chemically modified e.g., functionalized and derivatized to impart dispersancy as well as viscosity modification. The large size of the polymers of the MFVI enables them to significantly increase Kinematic viscosities of base oils even at low concentrations. However, because solutions of high polymer containing MFVI's are non-Newtonian, they tend to give lower viscosities than expected in a high shear environment due to the alignment of the polymer. Consequently, MFVI's impact (i.e., increase) the low temperature viscosities (i.e., CCS viscosity) of the base oil to a lesser extent than they do the high temperature viscosities. Accordingly, constraints are placed on the amount of V.I. improver which a formulator can employ for a given oil blend in order to meet the low and high temperature viscosity requirements of a target multigrade oil.
The aforesaid viscosity requirements for a multigrade oil can therefore be viewed as being increasingly antagonistic at increasingly higher levels of MFVI. For example, if a large quantity of MFVI is used in order to obtain high viscosity at high temperatures, the oil may now exceed the low temperature requirement. In another example, the formulator may be able to readily meet the requirement for a 10W30 oil but not a 5W30 oil, with a particular ad-pack (additive package) and base oil. Under these circumstances the formulator may attempt to lower the viscosity of the base oil, such as by increasing the proportion of low viscosity oil in a blend, to compensate for the low temperature viscosity increase induced by the V.I. improver, in order to meet the desired low and high temperature viscosity requirements. However, increasing the proportion of low viscosity oils in a blend can in turn lead to a new set of limitations on the formulator, as lower viscosity base oils are considerably less desirable in diesel engine use than the heavier, more viscous oils.
Further complicating the formulator's task is the effect that dispersant additives can have on the viscosity characteristics of multigrade oils. Dispersants are frequently present in quality oils such as multigrade oils, together with the V.I. improver. The primary function of a dispersant is to maintain oil insolubles, resulting from oxidation during use, in suspension in the oil thus preventing sludge flocculation and precipitation. Consequently, the amount of dispersant employed is dictated and controlled by the effectiveness of the material for achieving its dispersant function. A typical U.S. Service Station commercial oil contains four times as much dispersant as V.I. improver (as measured by the respective dispersant and V.I. improver active ingredients). In addition to dispersancy, conventional dispersants can also increase the low and high temperature viscosity characteristics of a base oil simply by virtue of its polymeric nature. In contrast to the MFVI, the dispersant molecule is much smaller. Consequently, the dispersant is much less shear sensitive, thereby contributing more to the low temperature CCS viscosity (relative to its contribution to the high temperature viscosity of the base oil) than a V.I. improver. Moreover, the smaller dispersant molecule contributes much less to the high temperature viscosity of the base oil than the MFVI. Thus, the magnitude of the low temperature viscosity increase induced by the dispersant can exceed the low temperature viscosity increase induced by the V.I. improver without the benefit of a proportionately greater increase in high temperature viscosity as obtained from an MFVI. Consequently, as the dispersant induced low temperature viscosity increase causes the low temperature viscosity of the oil to approach the maximum low temperature viscosity limit, the more difficult it is to introduce a sufficient amount of MFVI effective to meet the high temperature viscosity requirement and still meet the low temperature viscosity requirement. The formulator is thereby once again forced to shift to the undesirable expedient of using higher proportions of low viscosity oil to permit addition of the requisite amount of MFVI improver without exceeding the low temperature viscosity limit.
In accordance with the present invention, MFVI's are provided which have been found to possess inherent characteristics such that they simultaneously contribute less to low temperature viscosity increases and more toward high temperature viscosity increases than MFVI's of the prior art. Moreover, the advantages are obtained while still preserving the added benefit of dispersancy achieved by derivatization. This allows the formulator to back out more dispersant from the formulation by adding more MFVI than would otherwise be permitted in the absence of the beneficial high and low temperature properties.
U.S. Pat. No. 3,697,429 discloses a lubricating oil composition containing a viscosity index improver amount of an oil soluble polymer composition comprising first a copolymer of ethylene and a C.sub.3 to C.sub.18 olefin having an ethylene content of 50 to 95 mole percent (40-83 weight percent) and a second copolymer of ethylene in a C.sub.3 to C.sub.18 alpha olefin having an ethylene content of 5-80 mole percent (3-70 weight percent). The ethylene content of the first copolymer is at least 5 mole percent (four weight percent) more than the ethylene content of the second copolymer. By mixing the high and low ethylene copolymer a viscosity modifier with advantageous properties is made. The functionalization or derivatization of these polymers is not disclosed.
U.S. Pat. No. 5,068,047 discloses degraded ethylene copolymers of a certain specific type useful as viscosity index improver additives for oleaginous compositions. Said undegraded copolymers have a narrow molecular weight distribution and are comprised of segmented copolymer chains with compositions which are intramolecularly heterogeneous and intermolecularly homogeneous. These undegraded copolymers are segmented copolymers of ethylene and at least one other alpha olefin monomer. Each copolymer is intramolecularly heterogeneous and intermolecularly homogeneous and at least one segment of the copolymer constituting at least 10 percent of the copolymer chain is a crystallizable segment. The term "crystallizable segment" is defined to be each segment of the copolymer chain having a number average molecular weight of at least 700 wherein the ethylene content is at least 57 percent. The remaining segments of the copolymer chain are herein termed "the low crystallinity segments" and are characterized by an average ethylene content of not greater than 53 weight percent. These degraded copolymers may be grafted with various grafting materials to provide materials useful as multifunctional viscosity index improvers. Furthermore, the degraded grafted ethylene copolymer may be reacted with polyamines containing at least two reactive amine groups or polyols to provide materials useful as viscosity index improver dispersant additives for oleaginous compositions.
U.S. Pat. No. 4,735,736 discloses grafting oil soluble hydrocarbon polymers, useful as viscosity index improvers, such as ethylene-propylene copolymer with unsaturated acid materials such as maleic anhydride preferably by solid state grafting in a masticator or extruder followed by reaction with a polyamine, preferably a primary-tertiary polyamine. Although the use of amines having a single primary group such as primary-tertiary amine can reduce crosslinking and gelling particularly at relative high levels of maleic anhydride grafting, an undesirable high degree of viscosity increase may still occur. The further treatment and/or reaction with an aliphatic mono-amine represents a further improvement over prior art, wherein the viscosity increase can be further inhibited.
U.S. Pat. No. 4,780,228 discloses a further improvement in grafting of hydrocarbon polymers in the form of solid polymer in the substantial absence of any solvent or lubricating oil in an extruder or masticator. The grafting of the carboxylic acid e.g., maleic anhydride is done in the presence of a free-radical initiator and in the presence of a chain stopping agent e.g., aliphatic mercaptan which was found to prevent crosslinking of the polymer or the formation of insoluble gel. The product can then be subsequently reacted with an amine or alcohol in a subsequent reaction to form an oil soluble additive.
U.S. Pat. No. 4,517,104 discloses the grafting of ethylene-propylene-copolymer with maleic anhydride and peroxide in a lubricating oil solution. This is followed by addition of an alkenyl succinic anhydride, polyamines and optionally a capping agent.
Commonly Assigned copending application U.S. Ser. No. 989,289, filed Dec. 11, 1992 discloses the reaction of high or low ethylene-copolymers and mixtures thereof with maleic anhydride, peroxide and amination in an extruder.
U.S. Pat. No. 4,863,623 discloses the grafting of an ethylene-propylene-copolymer of 5,000 to 500,000 molecular weight with a carboxylic acid acylating material and is further derivatized with an amino aromatic polyamine compound from the group consisting of N-arylphenylenediamine, amino-thiazole, aminocarbazole, aminoindole, aminopyrrole, amino-indazolinone, amino mercaptotriazole and aminoperimidine.
U.S. Pat. No. 5,073,600 discloses grafting of ethylene-propylene-copolymer with a carboxylic acid material while the functionalization is performed in a high mechanical energy device in the presence of between 3 and 15 weight percent oil and further functionalizing the copolymer with an amine.
U.S. Pat. No. 5,055,213 discloses the reaction of copolymers having carboxylic functionality with phenothiazine derivatives.
U.S. Pat. No. 5,035,821 discloses multifunctional viscosity index improvers comprising the reaction products of ethylene-copolymers reacted or grafted with ethylenically unsaturated carboxylic acid moieties, polyamines or polyols and high functionality long-chain hydrocarbyl substituted dicarboxylic acid materials having a functionality of from 1.2 to 2 and a short-chain hydrocarbyl substituted dicarboxylic acid component.
U.S. Pat. No. 5,075,383 discloses an ethylene copolymer or terpolymer of a C.sub.3 to C.sub.10 alpha monoolefin and optionally a non-conjugated diene or triene having a number average molecular weight ranging from about 5500 to 50,000 with the copolymer molecular weight broken down in an extruder on which has been grafted in the absence of a solvent ethylenically unsaturated carboxylic acid function in a ratio of at least 1.8 moles of said carboxylic acid functions per molecule of said copolymer or terpolymer which is then further derivatized with an antioxidant amino aromatic polyamine compound from the group consisting of N-arylphenylenediamine, aminocarbozole, aminoindole, amino-indazolinane, aminomercaptotriazole and aminoperimidene.
U.S. Pat. No. 4,839,074 discloses a dual component lube oil flow improver which comprises a C.sub.14 dialkyl fumarate vinyl acetate interpolymer and a second component which comprises interpolymers of dialkyl fumarates and vinyl esters in which the fumarates are esterified with mixtures of C.sub.6 through C.sub.20 alcohols. The lubricating oil composition containing the lube oil flow improver may include a viscosity index improver as an optional third component. These viscosity index improvers are disclosed to be hydrocarbon polymers which may be degraded in molecular weight by mastication or extrusion, by oxidation or thermo-degradation and also included are derivatized polymers such as post-grafted interpolymers of ethylene-propylene with an active monomer such as maleic anhydride which may be further reacted with an alcohol or amine e.g., an alkalene, polyamine or hydroxy amine.
As demonstrated in the technical literature discussed above, it is of continuing importance to provide functionalized copolymers with improved stability, improved performance and improved utility in end use applications.
It is thus a principle objective to this invention to provide functionalized copolymers with improved properties that are useful in lubricating oil compositions as multifunctional viscosity modifiers.
Additional objectives will occur readily to those skilled in the art from the following specification which describes the invention in detail.